NAME

enc -- Encapsulating Interface

SYNOPSIS

To compile this driver into the kernel, place the following line in your
kernel configuration file:
deviceenc

DESCRIPTION

The enc interface is a software loopback mechanism that allows hosts or
firewalls to filter ipsec(4) traffic using any firewall package that
hooks in via the pfil(9) framework.
The enc interface allows an administrator to see incoming and outgoing
packets before and after they will be or have been processed by ipsec(4)
via tcpdump(1).
The ``enc0'' interface inherits all IPsec traffic. Thus all IPsec
traffic can be filtered based on ``enc0'', and all IPsec traffic could be
seen by invoking tcpdump(1) on the ``enc0'' interface.
What can be seen with tcpdump(1) and what will be passed on to the
firewalls via the pfil(9) framework can be independently controlled using
the following sysctl(8) variables:
NameDefaultsSuggested
net.enc.out.ipsec_bpf_mask 0x00000003 0x00000001
net.enc.out.ipsec_filter_mask 0x00000001 0x00000001
net.enc.in.ipsec_bpf_mask 0x00000001 0x00000002
net.enc.in.ipsec_filter_mask 0x00000001 0x00000002
For the incoming path a value of 0x1 means ``before stripping off the
outer header'' and 0x2 means ``after stripping off the outer header''.
For the outgoing path 0x1 means ``with only the inner header'' and 0x2
means ``with outer and inner headers''.
incoming path |------|
---- IPsec processing ---- (before) ---- (after) ----> | |
| Host |
<--- IPsec processing ---- (after) ----- (before) ---- | |
outgoing path |------|
Most people will want to run with the suggested defaults for
ipsec_filter_mask and rely on the security policy database for the outer
headers.

EXAMPLES

To see the packets the processed via ipsec(4), adjust the sysctl(8)
variables according to your need and run:
tcpdump -i enc0